Process for the production of poly(O-alkylurethanes) of the diphenyl methane series

Abstract

The present invention relates to an improved process for the production of monomeric and polymeric poly(O-alkylurethanes) of the diphenyl methane series. The process comprises the reaction of the corresponding amines with dialkyl carbonates in the presence of a catalyst, followed by the isolation of the products in a highly pure form. The invention also relates to the use of the produced monomeric and polymeric poly(O-alkylurethanes) for the production of the corresponding isocyanates.

We claim: 
     
       1. A process for the production of monomeric and/or polymeric poly(O-alkylurethanes) of the diphenyl methane series comprising reacting a) amines selected from the group consisting of 4,4'-diaminodiphenyl methane, 2,4'-diaminodiphenyl methane, 2,2'-diaminodiphenyl methane, higher homologs thereof formed in the condensation of aniline with formaldehyde, and mixtures thereof; with   b) a dialkyl carbonate containing from 1 to 2 carbon atoms per alkyl group; in the presence of     c) a catalyst; wherein said dialkyl carbonate is present in a quantity such that the molar ratio of dialkyl carbonate to amine is at least 40:1, and the formed monomeric and/or polymeric poly(O-alkylurethanes) crystallize out in a highly pure form upon cooling.     
     
     
       2. The process of claim 1, wherein said catalyst is a metal compound selected from the group consisting of Groups 1 to 15 of the periodic table. 
     
     
       3. The process of claim 1, wherein said catalyst is a metal compound selected from the group consisting of Group 12 of the periodic table, and Group 14 of the periodic table. 
     
     
       4. The process of claim 1, wherein said catalyst is a metal compound selected from the group consisting of tin, zinc, and lead. 
     
     
       5. The process of claim 1, wherein said formed monomeric and/or polymeric poly(O-alkylurethanes) are separated off after partial concentration of the reaction mixture. 
     
     
       6. In a process for the production of an isocyanate comprising heating a urethane, the improvement wherein said urethane is a monomeric and/or polymeric poly(O-alkylurethane) produced by the process of claim 1.